A gas containing volatile organic compounds (VOCs) such as hydrocarbons is generated from, for example, an off-shore crude oil tanker on loading the crude oil from a ground crude oil tank to the crude oil tanker. When crude oil is loaded to the crude oil tanker, the gas within the crude oil tanker is expelled. The gas inside the crude oil tanker is a gas generated from crude oil, and contains volatile organic compounds. The gas containing volatile organic compounds is generally emitted to atmosphere via a crude oil tanker-stack called the “vent”.
Further there is known a combustor which treats the gas containing volatile organic compounds by combustion. That type of combustor includes flare-stack and ground-flare. (Refer to Non-patent document 1.)    [Non-patent document 1] “Petroleum Handbook”, p. 462, (1988), edited by Nippon Oil Co., Ltd.